1. Field of the Invention
The present invention relates to a vehicle alternator which comprises magnets which are disposed between adjacent claw-shaped magnetic poles to minimize magnetic flux leakage between the claw-shaped magnetic poles.
2. Description of the Related Art
FIG. 11 is a perspective view of a claw-shaped magnetic pole from the rotor of the vehicle alternator described in Japanese Patent Laid Open No. HEI 4-255451. The claw-shaped magnetic pole 50, which faces the stator, has an approximately trapezoidal shape, which comprises a short side at the tip, a long side at the base, and two oblique sides, and magnets (not shown), which are each polarized in a direction which minimizes magnetic flux leakage between adjacent claw-shaped magnetic poles 50, are interposed between the side faces 50a of the claw-shaped magnetic poles 50. These claw-shaped magnetic poles 50 are constructed such that they satisfy the formula described below in order to prevent overcharging of a battery and to provide a vehicle alternator with high efficiency and high output: EQU 0.2.ltoreq.Br(L/W.multidot.COS.theta.).ltoreq.0.8
where Br is the residual magnetic flux density of each of the magnets (in tesla), L is the length of each of the claw-shaped magnetic poles 50 from the short side at the tip to the long side at the base, W is the width of the long side at the base of each of the claw-shaped magnetic poles 50, and 2.theta. is the angle formed by the two oblique sides.
Although the vehicle alternator of the above construction can prevent overcharging of the battery and provide a vehicle alternator with high efficiency and high output, the side faces 50a of the claw-shaped magnetic poles 50 are of a prescribed thickness t from the tip to the base, and the following problems arise:
(a) The magnetic flux generated in the rotor coil flows out to the stator through gaps while moving from the base to the tip of the claw-shaped magnetic poles 50. The claw-shaped magnetic poles 50 should therefore ideally be tapered and gradually become thinner towards the tip, but the thickness of the tip and the base of the claw-shaped magnetic poles 50 is the same, and the weight at the tip is therefore that much greater and the claw-shaped magnetic poles 50 are easily displaced outwards by centrifugal force; or PA1 (b) Generally, the claw-shaped magnetic poles are thin gradually towards the tip to account for the flow of the magnetic flux, but claw-shaped magnetic poles 50 of prescribed thickness from the base to the tip must be custom manufactured and production costs mount.